The Limits of Tornado Predictions

Storm watch: NOAA satellites send photos of storms to meteorologists for analysis. This image of the midwestern United States was taken during the April 2011 tornado outbreak.

The residents of Joplin, Missouri, had 24 minutes of warning before a tornado hit their city on Sunday. That gave many people time to take cover, but despite the warning, more than 100 people were killed. Meteorologists would like to be able to warn people earlier and perhaps save more lives, and they have gotten better at predicting the conditions that produce tornadoes. But the swift and chaotic nature of tornado formation might defy our technological capacity to forecast them with greater precision anytime soon.

The National Weather Service and its Storm Prediction Center issue two forms of tornado alerts: watches and warnings. Watches alert people to the presence of storm conditions that breed tornadoes, and can now be called up to five days in advance (10 years ago, warnings came three days in advance, at best). But watches only tell us that tornadoes might be coming—they’re not precise about when or where.

Tornado warnings, on the other hand, are issued when an eyewitness has reported a tornado, or when radar readouts indicate that a tornado is forming. Twenty years ago, residents would get a tornado warning five minutes before the event, on average. Now that time has grown to 15 minutes, on average. But it could be hard to keep extending that range.

Meteorologists already are devoting extensive resources to tornado predictions. They are honing mathematical models of thunderstorms and trying to better understand the conditions that cause those storms to produce tornadoes. The models require abundant data, such as patterns of temperatures and wind flow in the atmosphere, says Roger Edwards, a meteorologist with the National Weather Service. The data come from radar, lidar (light detection and ranging), and remote sensors. Additionally, the National Oceanic and Atmospheric Administration gathers atmospheric data from satellites. Those include geostationary satellites, which hover around 22,300 miles above Earth’s equator and snap images of weather in the Western Hemisphere, and polar orbiting satellites, which monitor changes in temperature, pressure, and other factors.

Back on Earth, meteorologists use many tools to assemble information about atmospheric conditions in tornado-prone regions. Radar and lidar help researchers measure the velocity of winds and thunderstorms. They can employ weather balloons and other unmanned aircraft equipped with sensors that collect data on air pressure, temperature, wind, and humidity.